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Articles 1 - 15 of 15
Full-Text Articles in Chemistry
Magnetic Properties Of The S=1/2 Quasisquare Lattice Antiferromagnet Cuf2(H2o)(2)(Pyz) (Pyz = Pyrazine) Investigated By Neutron Scattering, C H. Wang, M D. Lumsden, R S. Fishman, G Ehlers, T Hong, W Tian, H Cao, A Podlesnyak, C Dunmars, J A. Schlueter, Jamie L. Manson, A D. Christianson
Magnetic Properties Of The S=1/2 Quasisquare Lattice Antiferromagnet Cuf2(H2o)(2)(Pyz) (Pyz = Pyrazine) Investigated By Neutron Scattering, C H. Wang, M D. Lumsden, R S. Fishman, G Ehlers, T Hong, W Tian, H Cao, A Podlesnyak, C Dunmars, J A. Schlueter, Jamie L. Manson, A D. Christianson
Chemistry and Biochemistry Faculty Publications
We have performed elastic and inelastic neutron scattering experiments on single crystal samples of the coordination polymer compound CuF2(H2O)(2)(pyz) (pyz = pyrazine) to study the magnetic structure and excitations. The elastic neutron diffraction measurements indicate a collinear antiferromagnetic structure with moments oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60 +/- 0.03 mu(B)/Cu. This value is significantly smaller than the single-ion magnetic moment, reflecting the presence of strong quantum fluctuations. The spin wave dispersion from magnetic zone center to the zone boundary points (0.5 1.5 0) and (0.5 0 1.5) can be described by a …
Evidence That Aberrant Protein Metabolism Contributes To Chemoresistance In Multiple Myeloma Cells, Richard K. Sipes, Xue Xia, Brian S. Lewis, Nicholas E. Burgis
Evidence That Aberrant Protein Metabolism Contributes To Chemoresistance In Multiple Myeloma Cells, Richard K. Sipes, Xue Xia, Brian S. Lewis, Nicholas E. Burgis
Chemistry and Biochemistry Faculty Publications
Multiple myeloma (MM) is an incurable B lymphocyte cancer. To date, a comparative analysis of global protein metabolism for the MM cell line CCL-155 (RPMI-8226) and the non-cancerous B lymphocyte cell line CCL-156 (RPMI-1788) has not been published. Here, we report that both global protein synthesis and degradation occur at a higher rate in MM cells and demonstrate that alkylating agents can reduce global protein degradation in both cell lines, but the effect is greater in CCL-156 cells. Treatment with melphalan plus the proteasome inhibitor MG132 reduced global protein degradation for MM cells to roughly 60% of that seen without …
The Analysis Of Protein-Bound Thiocyanate In Plasma Of Smokers And Non-Smokers As A Marker Of Cyanide Exposure, Stephanie L. Youso, Gary A. Rockwood, Brian A. Logue
The Analysis Of Protein-Bound Thiocyanate In Plasma Of Smokers And Non-Smokers As A Marker Of Cyanide Exposure, Stephanie L. Youso, Gary A. Rockwood, Brian A. Logue
Chemistry and Biochemistry Faculty Publications
When cyanide is introduced into the body, it quickly transforms through a variety of chemical reactions, normally involving sulfur donors, to form more stable chemical species. Depending on the nature of the sulfur donor, cyanide may be transformed into free thiocyanate, the major metabolite of cyanide transformation, 2-amino-2-thiazoline-4-carboxylic acid or protein-bound thiocyanate (PB-SCN) adducts. Because protein adducts are generally stable in biological systems, it has been suggested that PB-SCN may have distinct advantages as a marker of cyanide exposure. In this study, plasma was analyzed from 25 smokers (chronic low-level cyanide exposure group) and 25 non-smokers for PB-SCN. The amount …
Time-Dependent Density-Functional-Theory Calculation Of High-Order-Harmonic Generation Of H-2, Xi Chu, Gerrit C. Groenenboom
Time-Dependent Density-Functional-Theory Calculation Of High-Order-Harmonic Generation Of H-2, Xi Chu, Gerrit C. Groenenboom
Chemistry and Biochemistry Faculty Publications
The observation of the isotope effect in the high-order-harmonic generation (HHG) of H-2 presents a challenge for time-dependent density-functional-theory (TDDFT) methods, since this effect is related to the dynamics of the ion created in the tunneling ionization step of HHG and it depends on the harmonic order. As an initial step toward describing this effect within current computational capacity, we benchmark a method in which the nuclear and electronic degrees of freedom are separated and both treated quantum mechanically. For the electrons two TDDFT formalisms are adopted. Although the ion-dynamics effect is not described in our method, it reproduces the …
Dimensionality Selection In A Molecule-Based Magnet, Paul A. Goddard, Jamie L. Manson, John Singleton, Isabel Franke, Tom Lancaster, Andrew J. Steele, Stephen J. Blundell, Christopher Baines, Francis L. Pratt, Ross D. Mcdonald, Oscar E. Ayala-Valenzuela, Jordan F. Corbey, Heather I. Southerland, Pinaki Sengupta, John A. Schlueter
Dimensionality Selection In A Molecule-Based Magnet, Paul A. Goddard, Jamie L. Manson, John Singleton, Isabel Franke, Tom Lancaster, Andrew J. Steele, Stephen J. Blundell, Christopher Baines, Francis L. Pratt, Ross D. Mcdonald, Oscar E. Ayala-Valenzuela, Jordan F. Corbey, Heather I. Southerland, Pinaki Sengupta, John A. Schlueter
Chemistry and Biochemistry Faculty Publications
Gaining control of the building blocks of magnetic materials and thereby achieving particular characteristics will make possible the design and growth of bespoke magnetic devices. While progress in the synthesis of molecular materials, and especially coordination polymers, represents a significant step towards this goal, the ability to tune the magnetic interactions within a particular framework remains in its infancy. Here we demonstrate a chemical method which achieves dimensionality selection via preferential inhibition of the magnetic exchange in an S = 1/2 antiferromagnet along one crystal direction, switching the system from being quasi-two-to quasi-one-dimensional while effectively maintaining the nearest-neighbor coupling strength.
Van Der Waals Density Functional Study Of Co2 Binding In Zeolitic Imidazolate Frameworks, Keith G. Ray, David Olmsted, Ning He, Yao Houndonougbo, Brian B. Laird, Mark Asta
Van Der Waals Density Functional Study Of Co2 Binding In Zeolitic Imidazolate Frameworks, Keith G. Ray, David Olmsted, Ning He, Yao Houndonougbo, Brian B. Laird, Mark Asta
Chemistry and Biochemistry Faculty Publications
The van der Waals density functional (vdW-DF) formalism is employed in a study of the binding energetics for CO2 in a set of five zeolitic imidazolate framework (ZIF) compounds. The ZIF structures investigated share the same RHO-type zeolite topology and metal atoms, but feature imidazolate linkers with different chemical functionalization. Three distinct binding sites are identified, for which the binding energies are found to show different dependencies on the functionalization of the linker molecules. The origin of the variations in the binding energies across the ZIF compounds is discussed through analyses of the binding geometries and charge-density distributions. A comparison …
Effects Of Carbon Chain Substituent On The P∙∙∙N Noncovalent Bond, U. Adhikari, Steve Scheiner
Effects Of Carbon Chain Substituent On The P∙∙∙N Noncovalent Bond, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The effects of carbon chains placed on the electron-accepting P atom of a P⋯N bond are examined via ab initio calculations. Saturated alkyl groups have a mild weakening effect, regardless of chain length. In contrast, incorporation of double bonds into the chain strengthens the interaction, Ctriple bond; length of mdashC triple bonds even more so. These effects are only slightly enhanced by additional conjugated double bonds or an aromatic ring. Placing F atoms onto the carbon chains strengthens the P⋯N bond, but only by a small amount, which wanes as the F atom is displaced further from the P along …
Contributions Of Various Noncovalent Bonds To The Interaction Between An Amide And S-Containing Molecules, U. Adhikari, Steve Scheiner
Contributions Of Various Noncovalent Bonds To The Interaction Between An Amide And S-Containing Molecules, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
N-Methylacetamide, a model of the peptide unit in proteins, is allowed to interact with CH3SH, CH3SCH3, and CH3SSCH3 as models of S-containing amino acid residues. All of the minima are located on the ab initio potential energy surface of each heterodimer. Analysis of the forces holding each complex together identifies a variety of different attractive forces, including SH⋅⋅⋅O, NH⋅⋅⋅S, CH⋅⋅⋅O, CH⋅⋅⋅S, SH⋅⋅⋅π, and CH⋅⋅⋅π H-bonds. Other contributing noncovalent bonds involve charge transfer into σ* and π* antibonds. Whereas some of the H-bonds are strong enough that they represent the sole attractive force in several dimers, albeit not usually in the …
Sensitivity Of Noncovalent Bonds To Intermolecular Separation: Hydrogen, Halogen, Chalcogen, And Pnicogen Bonds, Steve Scheiner
Sensitivity Of Noncovalent Bonds To Intermolecular Separation: Hydrogen, Halogen, Chalcogen, And Pnicogen Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
It is well known that noncovalent bonds are weakened when stretched from their equilibrium intermolecular separation. Quantum chemical calculations are used to examine and compare the sensitivity to stretches of hydrogen, halogen, chalcogen, and pnicogen bonds. NH3 was taken as the universal electron donor, paired with HOH and FH in H-bonds, as well as with FPH2, FSH, and FCl. Even though the binding energies span a wide range, stretching the intermolecular separation by 1 Å cuts this quantity by the same proportion, roughly in half, for each system. Taking the sum of van der Waals radii as an arbitrary cutoff, …
Preferred Configurations Of Peptide-Peptide Interactions, U. Adhikari, Steve Scheiner
Preferred Configurations Of Peptide-Peptide Interactions, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The natural and fundamental proclivities of interaction between a pair of peptide units are examined using high-level ab initio calculations. The NH···O H-bonded structure is found to be the most stable configuration of the N-methylacetamide (NMA) model dimer, but only slightly more so than a stacked arrangement. The H-bonded geometry is destabilized by only a small amount if the NH group is lifted out of the plane of the proton-accepting amide. This out-of-plane motion is facilitated by a stabilizing charge transfer from the CO π bond to the NH σ* antibonding orbital. The parallel and antiparallel stacked dimers are nearly …
Evaluation Of Dft Methods To Study Reactions Of Benzene With Oh Radical, Steve Scheiner
Evaluation Of Dft Methods To Study Reactions Of Benzene With Oh Radical, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Several density functional theory” (DFT) methods are applied to two different reaction channels involving OH• + C6H6, and the results compared with high-level ab initio calculations. The OH• adds directly to one C atom in the first channel, first forming an encounter complex with the OH• poised above the aromatic plane. B3LYP, BH&HLYP, and MPW1K compute an accurate estimate of the overall exothermicity, whereas M05-2X, PBE0, and PBEPBE overestimate this quantity to some degree. With the exceptions of PBEPBE and PBE0, the other methods produce an acceptable barrier to addition. All approaches except BH&HLYP correctly predict an exothermic H• abstraction, …
First Steps In Growth Of A Polypeptide Toward Β-Sheet Structure, U. Adhikari, Steve Scheiner
First Steps In Growth Of A Polypeptide Toward Β-Sheet Structure, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The full conformational energy surface is examined for a molecule in which a dipeptide is attached to the same spacer group as another peptide chain, so as to model the seminal steps of β-sheet formation. This surface is compared with the geometrical preferences of the isolated dipeptide to extract the perturbations induced by interactions with the second peptide strand. These interpeptide interactions remove any tendency of the dipeptide to form a C5 ring structure, one of its two normally stable geometries. A C7 structure, the preferred conformation of the isolated dipeptide, remains as the global minimum in the full molecule. …
Extrapolation To The Complete Basis Set Limit For Binding Energies Of Noncovalent Interactions, Steve Scheiner
Extrapolation To The Complete Basis Set Limit For Binding Energies Of Noncovalent Interactions, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
A means of extrapolating from double and triple-valence basis sets to a complete basis set is examined in the context of the pnicogen bonds in the BH2P⋯NH3 complexes, with B = CH3, H, NH2, CF3, OH, Cl, F, and NO2. Binding energies converge smoothly, and the trends for the various substituents B are unaffected by the basis set size, extrapolation, or level of inclusion of electron correlation, including MP2 and CCSD(T). The approach appears to be successful also for H-bonded systems, in particular the water dimer. In the event that full extrapolation within the context of CCSD(T) is not feasible, …
Botppi, A New Wittig Salt Used In The Synthesis Of 12-(S)-Hydroxy-Eicosatetraenoic Acid [12-(S)-Hete], Michael A. Christiansen, Merritt B. Andrus
Botppi, A New Wittig Salt Used In The Synthesis Of 12-(S)-Hydroxy-Eicosatetraenoic Acid [12-(S)-Hete], Michael A. Christiansen, Merritt B. Andrus
Chemistry and Biochemistry Faculty Publications
An efficient route to (Z)-(8-benzyloxy-8-oxooct-3-en-1-yl)triphenylphosphonium iodide, or BOTPPI, is disclosed, complete with full experimental details, NMR spectra, and HRMS data. BOTPPI serves as a surrogate for (Z)-(8-methoxy-8-oxooct-3-en-1-yl)triphenylphosphonium iodide, or MOTPPI, a Wittig salt previously used in two 12-HETE syntheses. BOTPPI has the advantage over MOTPPI of being derived from a sequence for which every intermediate is UV-active and amenable to large-scale chromatographic purification. A formal asymmetric total synthesis of 12-(S)-HETE is also reported, involving a stereoselective phase-transfer catalyzed (PTC) alkylation in its key step.
Detailed Comparison Of The Pnicogen Bond With Chalcogen, Halogen And Hydrogen Bonds, Steve Scheiner
Detailed Comparison Of The Pnicogen Bond With Chalcogen, Halogen And Hydrogen Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The characteristics of the pnicogen bond are explored using a variety of quantum chemical techniques. In particular, this interaction is compared with its halogen and chalcogen bond cousins, as well as with the more common H-bond. In general, these bonds are all of comparable strength. More specifically, they are strengthened by the presence of an electronegative substituent on the electron-acceptor atom, and each gains strength as one moves down the appropriate column of the periodic table, for example, from N to P to As. These noncovalent bonds owe their stability to a mixture in nearly equal parts of electrostatic attraction …